剑指offer18 --- 反转链表

剑指offer18 — 反转链表

题目

输入一个链表，反转链表后，输出新链表的表头。

分析

1. 将现有的头换成尾，尾部的next为空
2. 从第二个node开始，循环将next指向前一个
3. 需要有一个指针一直指向还没有反转的链表的头部

题目

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    # 返回ListNode
    def ReverseList(self, pHead):
        # write code here
        if pHead == None:
            return None
        if pHead.next == None:
            return pHead
        
        leftPointer=pHead
        midPointer=pHead.next
        rightPointer=midPointer.next
        leftPointer.next=None
        
        while rightPointer !=None:
            midPointer.next=leftPointer
            leftPointer=midPointer
            midPointer=rightPointer
            rightPointer=rightPointer.next
            
        midPointer.next=leftPointer
        return midPointer

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